The present invention relates generally to manufacturing systems. More specifically, the present invention relates to a method and system for calibrating an encoder and for the fabrication of a high resolution rotary encoder using interference lithography.
The demand for new products with more features in smaller areas has resulted in an increasing demand to manufacture smaller features at higher yields. The accuracy of the position information during manufacturing becomes more important in designing the manufacturing systems. For example, roll-to-roll processing has continued to be a preferred manufacturing method because of its cost-effectiveness. Therefore, the position/velocity accuracy in a roll process continues to present a challenge as ever smaller feature sizes are employed.
The position information for such systems is typically obtained from encoders. An optical encoder typically includes an encoder pattern, in the form of a grating, detectors and registration electronics. In a rotary encoder, the encoder pattern or the grating is typically written at the edge of disk on a planar substrate. Encoder patterns are often periodic structures, typically in the form of lines (i.e., similar to a grating structure) equally spaced apart from each other. The spacing of the lines used in the encoders can vary from hundreds of nanometers to tens of microns. Thus, the resolution of a rotary encoder is determined by its pitch and the length of its grating. Although a smaller line spacing is usually chosen for higher resolution, the accuracy in its line spacing can still be a limiting factor on the highest achievable resolution and accuracy for any given encoder. In fact, such commercially available encoders have inherent limitations in their resolution, their absolute accuracy and their repeatability. In addition, an external disturbance such as mechanical vibrations and temperature fluctuations perturbs the accuracy of the readings. Since conventional encoders are not located next to the substrate where manufacturing takes place, the external disturbances affect the position of the encoder and substrate differently. Therefore, the position readings obtained from the encoders does not reflect the actual position of the substrate to the degree of accuracy required for products with smaller feature sizes. The size of commercially available encoders are generally about 5-7 cm in radius. On the other hand, tape encoders may be written in long lengths through a step and repeat lithography techniques or some type of micro-replication printing process. However, this tape encoder when mounted to a cylindrical role will have a discontinuity at the splice.